Tap changer for transformers with elongated switch-over contact



Aug. 19, 1969 s NORMAN 3,462,562

' TAP CHANGER FOR TRANSFORMERS WITH ELONGATED SWITCH-OVER CONTACT 2Sheets-Shet 1 Filed Nov. 20. 1967 INVENTOR. sM/ERT Neg/1 Aug. 19, 1969s, NORMAN 3,462,562

TAP CHANGER F0 RANSFORMERS WITH ELONGATED SW H-OVER CONTACT Filed Nov.20, 1967 v 2 Sheets-Sheet 2 Fig.2

- INVENTOR. swear No 12M Ml United States Patent 'Ofifice 3,462,562Patented Aug. 19, 1969 TAP CHANGER FOR TRANSFORMERS WITH ELONGATEDSWITCH-OVER CONTACT Sivert Norman, Ludvika, Sweden, assignor toAllmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a Swedishcorporation Filed Nov. 20, 1967, Ser. No. 684,459

Claims priority, application Sweden, Nov. 21, 1966,

Int. Cl. Htllh 19/58, 21/78 US. Cl. 20011 7 Claims ABSTRACT OF THEDISCLOSURE BACKGROUND OF THE INVENTION Field of the invention Theinvention relates to tap changers of the selector switch type fortransformers.

Tap changers of the selector switch type where the closing and breakingunder load takes place in the selector itself are usually combined witha power accumulator, for example a spring driving device in order toensure rapid and safe operation.

In selector switches with plus/ minus switches it is necessary for theplus/minus switch to carry out its switching when the movable contact ofthe regulating selector leaves the fixed contact connected to the mainwinding of the transformer, the co-called switching contact, before itcloses the connection to the next fixed contact. In some constructionsthis problem has been solved by dividing the movement of the movablecontact of the plus/minus switch into two stages. However, the contactis then during a certain period situated in a position between the twofixed contacts of the plus/minus switch, with the regulating windingopen at both ends, so that dangerous voltages may occur between the twoends of the winding.

Another solution of the problem which is not completely satisfactoryeither is that the movable contact of the plus/minus switch performs itsswitching separately, driven directly by the driving motor of a springdevice, at the same time as the driving motor sets the spring device sothat the plus/minus switch is in its switched-over position when theenergy of the spring device is released for switching over the movablecontact of the regulating selector switch to an adjacent contact.However, even in this case there is a risk that the regulating windingwill be open if the movement of the driving device is not compelted tothe point where the spring energy is released, for example in manualoperation which is not completed or if for some reason the voltage ofthe driving motor should disappear.

There is also a risk with tap changers of the coarse/ fine connectiontype that the regulating winding will remain open in a certain positionof the change-over switch and also the disadvantage that almost theentire voltage of the regulating winding in certain control positionswill 'be between the movable contact of one of the contact fingers inthe regulating selector and a fixed contact of the regulating windingfor a distance which is considerably less than the distance between twofixed contacts.

SUMMARY OF THE INVENTION The above mentioned disadvantages arecompletely eliminated with a tap changer according to the inventionwhich relates to a tap changer for transformers comprising a regulatingselector with regulating winding and movable contact and also achange-over switch for switching over the connection of the main windingof the transformer to the regulating winding, where one of the fixedcontacts of the regulating selector, the switch-over con tact, isconnected to themain winding. The invention is characterized in that theswitch-over contact is elongated so that it covers substantially acomplete contact division of the regulating selector. During theconnection step following that in which the movable contact of theregulating selector moves over the switching contact, the movablecontact slides along the switching contact without any closing orbreaking of the current taking place. During this step the change-overswitch switches over and in known manner turns the voltage of theregulating winding in relation to that of the main winding. Since thespring driving device drives both the movable contact of the regulatingselector and that of the changeover switch, and since these two contactsare connected mechanically there is no risk that the regulating windingwill remain open for longer than the time taken by the switchingoperation itself. The power used during the switch-over will benegligibly more than during a normal connecting step since during thisconnecting step the contact of the regulating selector glides along theswitching contact and the necessary friction is negligible compared withthe switching operation in the change-over switch. The invention thusenables the use of smaller spring driving devices.

In selector switches having one shaft and fixed contact fingers on themovable contact, during a connection operation at least one of thesecontact fingers will be situated in the gap between two fixed contactsand the distance between such a contact finger and the neighbouringfixed contact will be considerably less than the distance between twofixed contacts. During a certain part of the plus/minus switchingoperation, therefore, the entire voltage of the regulating winding willlie across the said short-distance, with the consequent risk offlash-over. With the selector switch according to the invention only thestep-voltage can arise over said distance while the voltage of theregulating winding is over the distance between two fixed contacts.

BRING DESCRIPTION OF THE DRAWINGS In the accompanying drawings FIGURE 1shows the invention used for a tap changer with change-over switch.FIGURE 2 shows the invention used for a tap changer with coarse/ fineconnection and FIGURE 3 shows a third use of the elongated contactaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGURE 1 of the drawing themain Winding of the transformer is designated 1 and the regulatingwinding of the tap changer 2. The main winding is connected at one endto the movable contact 3 of the plus/minus switch. The ends of theregulating winding are connected to one each of the fixed contacts 4 and5 of the plus/ minus switch. The contact 4 is marked with and thecontact 5 with which means that when the contact 3 is in the shownposition the voltages of the two windings are in the same direction,plus-connection. The movable contact 3 is journalled on a shaft 6. Theregulating winding 2 has a number of fixed contacts 20, 21, 22, 23, 24,

25, 26, 27, 28 and 29 arranged in a circular path so that a movablecontact 7 at the centre of the circular path can cooperate with each ofthem. The regulating winding 2. with its contacts and the movablecontact 7 together form the regulating selector of the tap changer. Thedistance between each of the contacts 20-29 is preferably the same andis called a connection step. One end of the regulating winding 2 isconnected to the fixed contact 4 of the plus/minus switch and the otherend is connected to the contact 5. A switching contact 8 is arrangedbetween the contacts 20 and 29, the length of which corresponds to aconnection step and it is connected directly to the movable contact 3 ofthe plus/minus switch and thus also to the main winding 1.

The movable contact 7 in the regulating selector may be made indifferent ways, but in the shown embodiment it has a main contact 9 andtwo resistance contacts 10 and 11. The contact 10 is connected to themain contact 9 by a resistor 12 and in the same way the contact 11 isconnected to the main contact by a resistor 13. A conductor 14 isconnected to the movable contact 7 and to a point 15 which forms one endof the total phase winding. The other end of the phase winding isdesignated 16 and to this is connected the main winding 1.

The driving of the movable contacts 3 and 7 of the plus/minus switch andregulating selector, respectively, is coordinated and synchronized andtakes place in a way known in principle. A driving motor sets springs ina driving device and when the impulse to the switch arrives the springdriving device is released and the contact 7 of the regulating selectormoves forward one step. The contacts 3 and 7 are connected by means of aMaltese cross controlled by the contact 7 and influencing the plus/minusswitch during only one step corresponding to the switching contact 8.

If the contact 7 of the regulating reflector in the position shown inthe FIGURE 1 is moved one step in a clockwise direction the contact willslide on the switching contact 8 the whole time. When it starts to movethe contact 3 receives a driving impulse and snaps over to itsright-hand position. Thus during this connection step no switching overtakes place in the regulating selector, only a plus/minus switching. Thewhole regulating winding is then disconnected. During all otherconnection steps switching over takes place in the regulating winding.

In the position shown in the FIGURE 1 only one step of the regulatingwinding is connected between the contacts 8 and 29 and thus also betweenthe contact 8 and the resistance contact 10 on the movable contact 7.This voltage, step voltage, however, is so low that there is no risk offlash over. Between the contacts 8 and 20, however, is the entireregulating voltage, but since the contact 7 is at the left-hand edge ofthe contact 8, there is no risk of flashing over here either. Before thecontact 7 during the previously described connection operation hasreached the right-hand edge of the contact 8, the plus/minus has changedover and connected the contact to the contact 8 so that there is nowonly step voltage between the contacts 11 and 20. It is thus seen thatwhen full regulating winding voltage prevails between one of thecontacts 20 and 29 and the movable contact 7 with its resistancecontacts and 11, the distance across which said voltage lies is as greatas possible. This fact means that with the same diameter of regulatingselector this can be used for considerably higher voltages than haspreviously been the case.

The main contact 9 of the movable contact 7 consists of twospring-loaded contact tongues which grip the flat fixed contact 20-29and the switching contact 8, respectively, with considerable pressure inorder to obtain good contact and low transition-resistance. This meansthat considerable force is necessary at switching over to press the twocontact tongues apart so that they grip the stationary contact. This isalso the case for the plus/minus switch. in known constructions boththese operations take place simultaneously when the plus/minus switchingis to take place and the driving device must therefore be dimensioned sothat it is capable of switching both the contacts 3 and 9simultaneously.

FIGURE 2 shows a tap changer of the coarse/fine connection type. Theswitching contact 8 of the regulating selector is connected to a fixedcontact 4 belonging to the change-over switch. This fixed contact isalso connected to one end of the main winding 1 so that the switchingcontact 8 is permanently connected to the main winding. The other fixedcontact 5 of the change-over switch is connected to the main winding ata certain distance from the end which is connected to the contact 4. Themovable contact 3 of the change-over switch is journalled on the shaft 6and is also permanently connected to one end of the regulating winding2. Othewise the tap changer is identical in construction and function tothe type shown in FIGURE 1. Switching of the regulaing winding takesplace during a short time interval when the movable contact 7 of theregulating selector slides on the switching contact 8 and there is nooperating position when the regulating winding is open.

In a tap changer according to the invention, therefore, no more than oneswitching ever takes place simultaneously. When the change-over switchswitches from one position to the other the main contact 9 slides on theswitching contact 8, but the effort necessary for this movement isconsiderably smaller than was the case with known constructions, butstill operates satisfactorily.

FIGURE 3 shows another embodiment of the invention. As previouslymentioned the tap changer is moved from one end position past the centerposition where the change-over switch switches when the movable contact7 slides over the switching contact, and on to its other end position.The main contact 9 will then be situated on one of the fixed contacts 20or 29 of the regulating winding. One of the resistance contacts 10 or 11will then be in the gap between the switching contact 8 and the fixedcontact 20 or 29, on which the main contact 9 is situated. This meansthat almost the entire voltage of the regulating winding will lie acrossthe relatively short distance between the switching contact and one ofthe resistance contacts, with consequent risk of flash-over betweenthem. The figure shows how the two contacts nearest the switchingcontact are extended so that in the same way they extend aroundsubstantially a complete contact division of the regulating selector. Inthis last connection position, when the voltage of the regulatingwinding is between the switching contact 8 and one of the contacts 20 or29, the movable contact 7 of the regulating selector will be completelyacross one of the extended contacts 20 or 29 and have full insulatingdistance from the switching contact 8. There are cases, however, wherethe customer does not require more than, for example, 19 positions andin these cases nothing is lost.

I claim:

1. Tap changer for transformers including a regulating selector with aregulating winding and a movable contact and a change-over switch forchanging over the connection between the main winding of the transformerand the regulating winding, one of the fixed contacts of the regulatingselector constituting a switching contact connected to one end of themain winding of the transformer, said switching contact being elongatedand its length being greater than the distance the movable contact movesduring a complete switching step.

2. Tap changer according to claim 1, the fixed contacts of theregulating selector on both sides of and adjacent to the switchingcontact being elongated, the length of each of said two adjacentcontacts being substantially equal to the length of the switchingcontact.

3. Tap changer according to claim 1, in which the change-over switch isof plus/minus type with a movable contact connected to one end of themain winding of the transformer and two fixed contacts, one of saidfixed contacts being connected to one end of the regulating winding, thesecond of said fixed contacts being connected to the other end of theregulating winding, the movable contact of the regulating selector lyingon the switching contact during the time for the switching movement ofthe plus/minus switch.

4. Tap changer according to claim 1, characterized in that when themovable contact of the regulating selector is on the switching contactthe movable contact of the plus/minus switch is connected to the end ofthe regulating winding at which the distance between the movable contactof the regulating selector and one of the adjacent fixed contacts of thecontrol winding is least.

5. Tap changer according to claim 1 in which the change-over switch hasa movable contact which is connected to one end of the regulatingwinding and two fixed contacts which are connected to different outputsof the winding of the transformer, characterized in that the switchingcontact of the regulating selector is connected to one fixed contact ofthe change-over switch.

6. Tap changer according to claim 5, characterized in that the switchingcontact is connected to the fixed contact of the change-over switchconnected to one end of the transformer winding.

7. Tap changer according to claim 5, characterized in that one end ofthe regulating winding is connected to the movable contact of thechange-over switch.

References Cited UNITED STATES PATENTS ROBERT K. SCHAEFER, PrimaryExaminer ROBERT A. VANDERHYE, Assistant Examiner US. Cl. X.R.

